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dicttools.py

@@ -0,0 +1,39 @@
+_SORTED = sorted
+
+class Grouper(dict):
+
+    def plus(self, key, value_element):
+        try:
+            extant = self[key]
+        except KeyError:
+            self[key] = extant = []
+        extant.append(value_element)
+
+    def plusdate(self, key_value_pairs):
+        for key, value in key_value_pairs:
+            try:
+                extant = self[key]
+            except KeyError:
+                self[key] = extant = []
+            extant.append(value)
+
+def invert_mapping(mapping, single=False):
+    """Map from the values of `mapping` to their associated keys.
+
+       :param mapping: a dict whose values are hashable or containers of hashables.
+       :param single: True if values are to be keys in returned dict.
+       :returns: a dict mapping from the values (or values' elements) to collection of keys.
+       """
+    result = {}
+    for k,V in mapping.items():
+        iterable_V = [V] if single else V
+        for v in iterable_V:
+            try:
+                extant = result[v]
+            except KeyError:
+                result[v] = extant = set()
+            extant.add(k)
+    return result
+
+def sorted(dict):
+    return {key:dict[key] for key in _SORTED(dict)}